1. Field of the Invention
The present invention relates to a mist supplying device for applying an atomizing film-forming solution to a surface of a heated substrate to form a thin film of SnO.sub.2, In.sub.2 O.sub.3, TiO.sub.2, SiO.sub.2, or the like thereon.
2. Description of the Prior Art
FIG. 5 of the accompanying drawings illustrates a conventional apparatus for forming a thin film, the apparatus including a mist supplying device. The thin film forming apparatus has a reaction chamber 1 accomodating therein a plurality of substrates 2 with their surfaces to be coated with thin films being directed downwardly. The substrates 2 are fed through the reaction chamber 1 from right to left or left to right in FIG. 5. The substrates 2 are heated in the reaction chamber 1 to a temperature ranging from 400.degree. to 500.degree. C. by a heater 9 located behind the substrates 2. A nozzle 6 disposed downwardly of the substrates 2 in the reaction chamber 1 has an outlet port 7 toward the surfaces of the substrates 2. The nozzle 6 is coupled to an atomizer 4 and an air blower 5.
A film-forming solution to be applied to the substrates 2 is a solution of a chloride such as Sn, In, or the like. The solution is atomized in the atomizer 4 and fed to the nozzle 6 by the air blower 5. The atomized solution is then gradually applied from the outlet port 7 of the nozzle 6 to the surface of the substrates 2. Part of the atomized solution is dehydrated and vaporized by absorbing heat in the vicinity of the surfaces of the substrates 2. The vaporized solution reacts with oxygen and water vapor to form an oxidized film of SnO.sub.2, InO.sub.3, or the like which is attached to the surfaces of the substrates 2.
The thin film of SnO.sub.2 or InO.sub.3 is transparent. Therefore, if the deposited thin film is irregular in thickness, it will produce varying electric resistances and dielectric constants, and also form interference fringes that make the film poor in appearance. With a view to forming a thin film of uniform thickness, there has been attempted to provide a screen 8 in the nozzle 6 for evenly dispersing the atomized solution to apply the same uniformly to the surfaces of the substrates 2.
In the thin film forming apparatus shown in FIG. 5, the atomized solution is supplied onto the surfaces of the substrates 2 while the substrates 2 are being progressively delivered from right to left or left to right as shown. Thus, the film thickness is less likely to become irregular in the direction in which the substrates 2 are fed.
However, there is a greater tendency for the deposited film to have thickness irregularities in a direction perpendicular to the direction of feed of the substrates 2 due, for example, to a localized flow of the atomized solution from the atomizer 4, which may happen even if the screen 8 is present. Such thickness irregularities are apt to produce interference fringes along the direction of feed of the substrates 2.